The present invention relates to the food and flavor industry. It concerns more particularly a complex coacervation process for the preparation of microcapsules which can be “Halal” certified. The process of the invention is based on the use of type B gelatin as positively charged polymeric wall material.
Coacervation, also called aqueous phase separation, is a very well known technique for encapsulating hydrophobic liquids. A coacervation process allows to provide oil-containing microcapsules, the encapsulating material being a gelled hydrophilic colloid that is impervious to the oil and deposited evenly and densely about the oil as nucleus. The encapsulating material is a protein which may be complexed with another colloid having an opposite electric charge.
A coacervation process essentially involves an aqueous protein solution which is manipulated by changing the physico-chemical environment (dilution and/or adjustment of pH) to result in phase separation of the protein from the solution to varying degrees depending on the molecular weight of the protein, its isoelectric point and compatibility with solvents.
A coacervation process may be “simple” or “complex”. The former designation is employed when a single protein is used to form a capsule wall as phase separation is taking place. The latter term designates the use of a second oppositely charged non-protein polymer to bring about phase separation. Complex coacervation method is widely practiced in commercial processes and has been well described in the literature. In particular, U.S. Pat. Nos. 2,800,457 and 2,800,458 disclose complex coacervation in a very detailed manner.
Generally, a coacervation process comprises four basic steps consisting in respectively emulsification, coacervation, wall formation and wall hardening. In a complex coacervation process the wall surrounding the core material is, as mentioned above, constituted of two oppositely charged high molecular weight colloids. In most of the cases, the positively charged colloid used is gelatin, a functional protein derived from collagen by hydrolysis and subsequent extraction. There are two commercially available food/pharmaceutical grade gelatins, designated as “type A” and “type B”. The primary difference between the two grades, arises from the manufacturing process. If the collagen source is hydrolyzed by an acid, the final product gets a designation “A” and if it is done by a liming (base) it is designated “B”. From a product standpoint, the two gelatins differ primarily in their isoelectric points. Type A has an isoelectric point of 8.5 to 9.0 while type B has 4.8 to 5.5. In a process such as coacervation that predominantly depends on the eletrokinetic stability of the system, such difference in isoelectric points can be critical for successful encapsulation.
The prior art related to complex coacervation almost always describe the use of type A gelatin as a cationic protein wall. The pH during the process is therefore kept to values inferior to the isoelectric point of the latter in order to have it positively charged. Some documents from the prior art mentions the possibility to use gelatin provided by basic hydrolysis as a cationic protein wall, but to our knowledge, no example has ever described such an embodiment and it has been established that the processes disclosed in the prior art do not allow the preparation of satisfactory microcapsules when type B gelatin is used as protein wall, in its cationic form. On the other hand, type B gelatin is sometimes mentioned in complex coacervation processes as being used as polyanionic polymer i.e. in its electronegative form, in combination with a type A gelatin as positively charged colloid.
Now, as with many food ingredients, there are some regulatory constraints on gelatin uses, from a religious/ethnic standpoint. This includes “Kosher” and “Halal” status of gelatin. Generally, type A gelatin manufacturing process uses pig skin as starting material. As a consequence the microcapsules produced from this starting product cannot receive the “Halal” or “Kosher” status. Type B gelatin, on the other hand, issued from cows, could receive this certification. However, no complex coacervation process disclosed in the prior art to date technically allows the preparation of microcapsules based on type B gelatin.
Now, we have been able to establish a novel coacervation process suitable for the preparation of microcapsules based on type B gelatin as cationic wall material.
Varaporn Buraphacheep Junyaprasert et al. describe in Drug Development and Industrial Pharmacy, 27(6), 561-566 (2001), a complex coacervation process for the encapsulation of Vitamin A, which uses type B gelatin in combination with gum acacia as wall materials. However, the process parameters there-disclosed are not optimized, in particular, the drug contents of the microcapsules do not exceed 50% w/w.
The process according to the present invention allows to overcome the drawbacks observed in the prior art by providing an optimized complex coacervation process suitable for the preparation of microcapsules susceptible of being “Halal” certified, and containing up to 80% w/w of hydrophobic core material.